Recently, it has been stated that ultraviolet rays accelerate skin aging, and in order to protect skin from ultraviolet rays, cosmetics and skin care products for external use, each containing an ultraviolet rays absorber and a ultraviolet rays scattering agent, have been frequently used. Titanium dioxide, in particular, titanium dioxide microparticles, are mainly used as the ultraviolet rays scattering agent. Various shapes such as a solid powder, milky lotion, oil, etc. are blended according to objects thereof. Most of these sun care products are W/O type emulsified cosmetics using surfactants.
The ultraviolet rays care effect of the sun care product compositions is mainly obtained by reflecting ultraviolet rays with titanium dioxide microparticles contained in the cosmetics. Therefore, in order to reflect ultraviolet rays more efficiently, the cosmetics containing titanium dioxide are required to become homogeneous on skin after applied, and keep that state. Generally, emulsion type cosmetics have features that the water content after applied evaporates or penetrates through skin, and a remaining oily component and dispersed titanium dioxide remain on skin homogeneously and closely adhere thereto.
The emulsion type cosmetic, however, contains a surfactant in order to emulsify components thereof, so that, when sweating, sweat and the surfactant blend into each other, and further, the surfactant, oily component and titanium dioxide blend into each other. Consequently, the homogeneity of titanium dioxide on skin is degraded with sweat. When the homogeneity is thus degraded, and titanium dioxide becomes inhomogeneous on skin, the reflectance of the ultraviolet rays remarkably drops so that the operation as the ultraviolet care cosmetic cannot be achieved.
Under the above circumstances, many sun care product compositions adopt a W/O type emulsion, and by mixing a high viscosity silicone that is difficult to blend with the surfactant, the surfactant locally exists inside the W/O type sun care product composition, whereas the high viscosity silicone locally exists in an outermost part thereof, and consequently, the surfactant is prevented from blending with sweat. Thus, the water resistance of the sun care product composition is improved, and even if sweating, the homogeneity of titanium dioxide on skin is maintained, and consequently, the ultraviolet rays care effect continues for a sufficient period of time.
However, when the water resistance is improved in this manner, the cosmetic becomes difficult to be washed away by normal washing methods using soaps and face cleansing foams. And in order to remove the sun care product compositions, they have been wiped out by oils for use in wiping, and then washed away using soaps or face cleansing foams. Where general adult women use the sun care product compositions on their faces, by cleansing them with the above-described two steps, troubles caused by remaining sun care product compositions can be reduced, but where the ultraviolet rays protective cosmetics are applied to arms and foots, or children use the same, in many cases, the ultraviolet rays protective cosmetics have been tried to remove only by washing with soaps, and consequently, it has been difficult to remove the ultraviolet rays protective cosmetics sufficiently. As a result, it becomes insufficient to clean the ultraviolet rays protective cosmetics so that they remain in pores, etc. in skin, to cause rough skin, skin eruptions, etc. In addition, as described above, the conventional ultraviolet rays protective cosmetics have been intended to improve the water resistance, while sacrificing the readily washing properties thereof, so that many of the ultraviolet rays protective cosmetics have exhibited good water resistance, but have not been readily washed away.
Under the above circumstances, O/W type cosmetics which are emulsified with an emulsifying method using no surfactant have been considered as the cosmetics which are readily washed away with a normal washing method using soaps and cleansing foams. The technique of emulsifying oily components by use of the technique such as nanodispersion, etc. has been known as the emulsifying method without using any surfactant (see Non patent documents 5, 6 and Patent document 1, for example). This technique means the three-phase emulsifying method of carrying out emulsification by making nanoparticles of polysaccharide, which exist in a system of oil/amphipathic chemical compound/water as an independent phase adhere to surfaces of oily components with van der Waals' force. This emulsification is excellent as the emulsifying method with which the emulsion stability of the components to be emulsified, such as oily components, etc. is maintained for a long period of time without adding any surfactant or any substance exhibiting substantially surface active performance.
However, the emulsion-dispersing of the titanium dioxide microparticles, which serves to achieve the ultraviolet rays protective effect, has not been sufficient. The reason is that the titanium dioxide microparticle blended in the cosmetics has light activity so that in order to prevent the titanium dioxide microparticle from directly contacting skin for improving safety, the surface of the titanium dioxide microparticle has been coated with various kinds of inorganic compounds and organic compounds.
Many kinds of chemical compounds have been used for coating, and examples thereof include aluminum hydroxide, stearic acid, hydrous silicic acid, dimethylpolysiloxane, methyl-hydrogen-polysiloxane, etc. By blending titanium dioxide subjected to the surface treatment with these chemical compounds, for example, with polysaccharide to be used in the present invention, cosmetics exhibiting ultraviolet rays preventive actions and good touch can be obtained, but, where the constituent monosaccharide of the above-described polysaccharide is glucuronic acid having carboxyl groups, the available surface treatment for titanium dioxide is limited.
Namely, when polyhydric metal ions or polyhydric metal ion chemical compounds are contained in the surface treatment of titanium dioxide, metal ions dissolve out with time, even if a very small amount is contained. The dissolved polyhydric metal ions combine with carboxyl groups of the polysaccharide to provide aggregation to the polysaccharide. The polysaccharide having aggregating power gradually become tight, the cosmetics homogeneously emulsified become solid, and water may be separated therefrom. And, if polyhydric metal is not contained as a surface treating agent, similar phenomena may occur where a polyhydric metal-based surface treating agent is used in the surface treatment step, and a residue thereof is intermixed therein.
Therefore, in the surface treatment step of titanium dioxide, sodium silicate solution is directly reacted with titanium dioxide powder. Otherwise, it becomes necessary to use a titanium dioxide microparticle subjected to the heat treatment, which does not contain polyhydric metal, by using the method of performing the surface treatment with hydrous silicic acid and a hydrous silicate compound after the surface treatment with methyl-hydrogen-polysiloxan.
The cosmetic contains various many components according to the kind thereof, and, for example, contains organic solvents, oils, moisturizer, astringents, bleaching agents, UV preventive agents, oxidation preventive agents and perfumes as oily components. The oily components have the cleaning effect, water-retaining effect, emollient effect and protective effect against skin, and perform the functions of improving the spreading ability, smooth feeling, glossiness, adhering properties, etc. of the cosmetic.
Where the oily components as components to be emulsified, which are contained in this cosmetic, are used in the cosmetic, conventionally, these components have been emulsified and dispersed in purified water, using surfactants.
In the case of the oily components, the surfactants have been selected according to required HLB values thereof and characteristics of surfaces of granules, and the emulsification and dispersion have been carried out using many kinds of surfactants. The required HLB values of the surfactants adapted to be used as an emulsion-dispersing agent must be made different between the case of oil-in water (O/W) emulsions being produced and the case of water-in-oil (W/O) emulsions being produced, and the thermal stability and storage stability are not sufficient so that many and various kinds of surfactants have been used as a mixture thereof (see Non patent documents 1 through 4, for example).
The conventional emulsifying method using surfactants is based on the technique of adsorbing surfactants on interfaces between oil and water to decrease surface energy therein so that a large amount of emulsifiers (surfactants) have been needed to reduce an interfacial tension thereof.
The surfactants, however, are low in biodegradation to cause bubbling, and accordingly, exhibit the problems such as environmental pollution so that the reduction of the amount of the surfactants has been required.
And emulsifiers for oily components have been generally prepared by physicochemical emulsifying methods such as the HLB method, phase inversion emulsifying method, phase transition temperature emulsifying method, gel emulsifying method, etc, and in these methods, the emulsions have been prepared by decreasing surface energies in oil/water interfaces to stabilize systems thermodynamically. Therefore, in order to select the emulsifiers mostly suited to the cosmetics, very troublesome and lots works have been needed, and since, in the cosmetics, many kinds of oily components are mixed therein, stable emulsification thereof has been frequently difficult.
In addition, the cosmetics are required to exhibit many and various effects so that it is needed to stabilize many substances (components to be emulsified) exhibiting various surfacial tensions in a single cosmetic. In particular, silicone oil is chemically stable, safe with substantially no reactivity, odorless with little stickiness, has a low surface tension with good spreading ability, and has smooth feeling so that it has been blended in many cosmetics such as creams, milky lotions, lotions, gels, etc.
However, since silicone oil is very hydrophobic and the interfacial tension thereof is low, it has been difficult to stabilize silicone oil in aqueous solutions. And where the surfactants adapted to emulsify silicone oil are used, there has occurred the problem that emulsification of organic acids such as stearic acid, etc. and higher alcohols such as cetanol, etc. becomes instable, and in the case of the substances such as titanium dioxide particles and iron oxide particles, of which surfacial tensions are extremely different from that of organic compounds being used in the cosmetic, there has occurred the problem that emulsification becomes more difficult.
And when a large amount of oily component is intermixed with water, there occurs a phase transition in “type” of the emulsion, and where the surfactant is used, an oily component phase and a water phase may separate from each other.
Under the above circumstances, in order to solve the problems concerning the emulsification with the use of surfactant, the technique of emulsifying oily components without adding any surfactant using the technique such as nanodispersion, etc. has been known (see Non patent documents 5, 6 and Patent Document 1, for example).
This technique means the three-phase emulsifying method of carrying out emulsification by making a nanoparticle that exists in a system of oil/amphipathic chemical compound/water as an independent phase adhere to a surface of an oily component with van der Waals' force. This emulsification is excellent as the emulsifying method, because no surfactant (including substance having a substantially surface active performance) is added, and the emulsion stability of the components to be emulsified, such as the oily component, etc. is maintained for a long period of time.
However, the cosmetics prepared by using this technique were bad feelings so as not to be practical. Namely, when the cosmetics are used actually, as shown in FIG. 1, the oily components deform due to pressure of fingers, etc. and friction forces against skin upon applying them to the skin, and consequently, van der Waals' force between nanoparticles and the oily components decreases or disappears, whereby the nanoparticles separate from surface of the oily component. As a result, the oily components dispersed coalesce with each other on skin to become large oil drops to separate from water. The thus separated oily components exist on skin as drops to degrade the skin absorbent. Therefore, in order to improve the blending properties into skin of the cosmetics prepared by the three-phase emulsifying method, surfactants or chemical compounds having substantially surface-active effect, such as phospholipid including hydrogenated lecithin, ceramido derivative including sphingolipid have been added so that the cosmetics containing no surfactant have not been able to be produced.    Non patent document 1: “Emulsion Science” Edited by P Sherman, Academic PressInc. (1969)    Non patent document 2: “Microemulsions-Theory and Practice-Edited by Leon M. price, Academic Press Inc. (1977)    Non patent document 3: “Technique of Emulsification and Solubilization” edited by Susumu Tsuji, Kougakutosho Ltd. (1976)    Non patent document 4: “Developing Technique of Functional Surfactants” published by CMC Publishing Co., Ltd. (1998)    Non patent document 5: Abstract of The 43th Annual Meeting of the Japan Oil Chemists' Society, Oosaka University, Convention Center (Nov. 1-Nov. 2, 2004)    Non patent document 6: Abstract of The 57th Meeting on Colloid and Interface Chemistry of The Chemical Society of Japan (Sep. 9-Sep. 11, 2004)    Patent document 1: Patent application laid open No. 2004-130300